1. Field of the Invention
The present invention relates to a container for transporting precision substrates, which is for accommodating in its inside precision substrates such as semiconductor wafers (also referred to wafers hereinafter), magnetic disks or the like, and useful for protecting the substrates from damages and contamination, as well as reliable storage and transportation of the substrates.
2. Description of the Related Art
Conventional containers for transporting precision substrates consist of, as shown in FIG. 7, a container body 2 having an upper open periphery, a cassette 4 to be accommodated in the container body 2 for holding a plurality of precision substrates W in parallel, a top covering 3 mountable on the container body 2 which is fitted to the open periphery 9 of the container body via a gasket 5, and a substrate presser (retainer or cushion member) 6 attached inside the top covering 3.
Further, a pair of hooks 7 extending downward are provided around an open periphery of the top covering 3 and a pair of locking members (clamping member) 8 are provided around the open periphery of the container body 2 for locking the hooks 7. The transportation container 1 can be closed by putting the top covering 3 on the container body 2, and locking the hooks 7 with the locking members 8 so as to bring the top covering 3 into close contact with the container body 2 via the gasket 5.
A skirt flange 10 is further provided around the open periphery 9 of the container body in order to reinforce the open periphery 9 and to protect the locking members 8 by absorbing an externally applied force. The skirt flange 10 is useful also as a grip when the transportation container 1 is handled by hand.
In recent years, degree of cleanliness required for precision substrates such as semiconductor wafers has been becoming higher and higher, as semiconductor circuits become increasingly finer. Therefore, high quality has been required with regard also to cleanliness of the transportation container. Upon use of a transportation container, the container is thoroughly cleaned by hand with a cleaning solution such as those containing surfactant and rinse such as pure water and super-pure water to remove contamination source such as particles from the surface of the container before use. Further, although such a transportation container has frequently been thrown away after use heretofore, it has become to be reused in view of cost reduction, resource saving, and environmental problems, as the container becomes larger with the use of larger diameter substrates or increased number of substrates to be accommodated therein.
Moreover, in recent years, because the transportation container has become to be cleaned and dried under a more highly clean environment for improving the cleanliness and stabilization thereof, treatment process steps such as cleaning, drying and transporting by a series of automatic apparatuses has been increased.
As mentioned above, the cleaning process has become increasingly important in order to keep the quality of transportation containers of precision substrates upon their use. While the cleaning has conventionally been conducted by hand in many cases, it invited a problem that the quality of cleaning could not be constant as larger transportation containers have become used. In particular, reusable containers are likely to be adhered with many particles, and contamination degree thereof may be fluctuated. Therefore, automatic cleaning apparatuses have become to be used for cleaning of reusable transportation containers in order to stabilize the quality of cleaning. However, another problem was arisen that when cleaned transportation containers are dried automatically, the containers should be placed so that their open periphery should face downward, and during this process a lot of water remains between the skirt flange and the side wall of the containers. Accordingly, it took a long period of time to dry them, and hence the productivity was degraded. Further, when water remained at the flange portion, this portion could not be cleaned sufficiently, and therefore particles and the like became likely to remain, which may be a cause of contamination of substrates to be accommodated. In order to solve these problems by the design of the apparatuses, a new processing unit suitable for the shape of the transportation containers, for example, an apparatus for inverting the container body, should be provided. This restricts applicability of the apparatuses, and invites increase of equipment cost and thus cleaning cost.
In order to provide a hole or slit on the side of the flange portion to prevent the retention of water, it is necessary to provide a special sliding mechanism in metallic molds for molding the transportation containers, because the hole or slit may interfere with the release of molded containers from the metallic molds. This might increase the cost of the metallic molds.